1. Field of the Invention
The present invention relates to a disk drive, and more particularly, to a method and apparatus for compensating offset of a disk drive.
2. Description of the Related Art
In general, a hard disk drive reproduces data recorded on a disk or writes user data to a disk using a magnetic head. As the hard disk drive has high capacity and high density while being made compact, BPI (bit per inch) that is the density of data in a rotational direction of the disk and TPI (track per inch) that is the density of data in a radial direction of the disk increase so that a more accurate control mechanism is needed.
The drive repeats track following and search operations to store information. In doing so, a spindle motor is rotated at a constant speed to lift the head to a predetermined height above the disk. For an embedded method, position information needed for the track following and search operations is written to the disk in a servo pattern having a period corresponding to a servo sampling frequency. The servo pattern is written by a servo writer. In some cases, a servo copy process is provided to obtain a high quality servo pattern signal.
The servo writer theoretically employs a motor speed control system that is the same as that for the spindle motor. A motor speed control circuit used for the servo writer and a PCBA circuit used for an actual drive may be different in a device value and DAC offset for a motor. Accordingly, the rotation speed of the spindle motor can vary by a few r.p.m., compared to a designed rotation speed.
However, in a conventional offset compensation method. In order to prevent reproduction failure due to a change of a frequency during reproduction, while a change in the speed of a motor during writing data to a disk is continuously monitored, a writing operation is allowed only when the speed of a motor has a value within a particular range from a target speed. Thus, since the conventional offset compensation method allows writing only when spin jitter exists within a writing operation allowance standard, the writing performance of a drive is deteriorated in the process of considering the offset.